A trench capacitor is a common element in various semiconductor devices, such as DRAM devices, for example. Dynamic random-access memory (DRAM) cells are composed of two main components, a storage capacitor that is used to stores electronic charge and an access transistor that is used to transfer the electronic charge to and from the storage capacitor.
The storage capacitor may be either planar on the surface of the semiconductor substrate or trench etched into the semiconductor substrate. In the semiconductor industry where there is an increased demand for memory storage capacity accompanied with an ever decreasing chip size, the trench storage capacitor layout is favored over the planar type, and is the prevailing design choice today.
A trench DRAM cell comprises a trench capacitor and a transistor. The trench capacitor typically is comprised of a cavity etched into the substrate, a first electrode—often referred as a “buried plate”—in the substrate, a second electrode in the trench, a thin node dielectric which separates those two electrodes. The transistor is formed above the trench capacitor. A dielectric isolation collar is formed in the upper region of the trench to suppress undesired parasitic leakage between the transistor and the capacitor. The collar is an important part of the DRAM cell, as it serves to prevent the effects of undesired parasitic leakage from occurring.
To compensate for the effects of the undesired parasitic leakage, the collar must be sufficiently thick to prevent the undesired parasitic leakage from having a significant effect on the circuitry of the semiconductor device. As the feature size scales down, this causes a reduction in the amount of trench conductor that can be used, thereby increasing the trench resistance, and reducing the performance of the device. Therefore, it is needed to have an improved trench capacitor that is highly scalable, while still providing high performance for today's electronic devices.